Talk:Luminous efficacy

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[edit] Example: Electroluminescent devices

Another example I would find interesting is electroluminescent devices. Night light panels often draw on the order of 0.05W or less but that appears to be due to very low output rather than good efficiency. The web browsing I have done so far suggests 3lm/W or less for panels; I have been unable to find a source for EL "wire".

—The preceding unsigned comment was added by 63.193.211.225 (talk) 16:05, 15 December 2006 (UTC).

[edit] Spelling

Is 'Luminous efficacy' correctly spelled, or is 'efficacy' some word with special meaning? Electron9 09:13, 11 January 2007 (UTC)

See definitions. Dicklyon 20:57, 11 January 2007 (UTC)

[edit] Merge Lighting efficiency?

Since nobody supported this idea, I'm removing the merge tag. Dicklyon 04:10, 10 July 2006 (UTC)

The merge seems like an obvious good idea to me. On the whole, Luminous efficacy is a better article (gives sources, has more details). Kingdon 20:39, 14 September 2006 (UTC)
As a reminder, the old (June 06) proposal was to merge Lighting efficiency into here; I just noticed that that the other article still has its mergeto tag. It seems like a very distinct topic to me, focusing on practical light sources as opposed to the concept. But they could be integrated if someone was motivated to work on that. Dicklyon 22:14, 14 September 2006 (UTC)
Oppose. The more I look at it the more separate the concepts seem. We should explain that. The efficacies and efficiencies in this article are purely photometry/radiometry relationships on spectra. The lighting efficiency of the other article is with respect to power consumed, not power radiated, and includes effects of energy loss via conduction and convection, if I understand correctly. Dicklyon 22:33, 14 September 2006 (UTC)
This article covers that too. The section on Overall luminous efficacy explicitly deals with efficacy and efficiency of light emission as a function of input electrical power, i.e. including the effect of losses due to conduction, convection, heat, etc.--Srleffler 00:06, 15 September 2006 (UTC)
The overlap is quite strong, and each has tabulated information that the other is lacking. The main difference between the two is mere emphasis. This article focuses on the technical definition of luminous efficacy/efficiency, and compares the standard and "overall" types in one article. The other article focuses more on the practical issue of how efficient a given lighting technology is. Both foci seem useful--one for those interested in photometry, and one for those who want to know more about light bulbs. If anything, I think we should probably split and merge the other way: move the overall efficacy/efficiency information into the other article, keeping the practical layman's terms approach in the introduction and providing a more technical explanation with links between the two articles. This article could be limited to the "true" luminous efficacy/efficiency, with some explanation of the distinction between this and the overall value and links to the other article.--Srleffler 00:20, 15 September 2006 (UTC)
That kind of split makes sense to me. The key thing would be having the two articles link to each other cleanly, and cutting down on the material which is duplicated. Kingdon 14:20, 15 September 2006 (UTC)
I don't see the need for two articles here. This article needs at lease some examples to make sense and there is is no reason to have the information in two places. I support the original merge.--agr 14:07, 21 September 2006 (UTC)

There doesn't seem to be a consensus one way or another here, so I've tried merging the pages, and we'll see if the result is acceptable. This article is not really much changed, and I think the changes are largely ones we would want to keep even in the absence of a merge. The major change is that lighting efficiency now redirects here. I think this is best, since "lighting efficiency" as defined there was really just the overall luminous efficacy, as defined here. It seems better to have one article that explains it all in context, rather than two. I'm certainly open to splitting off the "Lighting efficiency" section of the merged article, and moving that back to "lighting efficiency" with appropriate links, if that seems better to most people.--Srleffler 06:02, 25 September 2006 (UTC)

[edit] Xenon Lamp efficiency?

Am yet to see any xenon lamp rated at 150lm/W. Osram XBO line for example has a maximum of 500000lm per 10000W, that's 50lm/W. I would like to see a model rated above 60lm/W in any catalog. Most such lamps are below that, at about 40lm/W. Unless I see any new data I'll correct the article in the next few days. --Rnbc 02:38, 22 February 2007 (UTC)

Read the reference.[1] The lamp with 150 lm/W is clearly a specialty item, with 20 kW total power consumption. The largest XBO bulb is only 12 kW. The efficiencies given in the reference agree with the XBO datasheet for the 1 kW and 5 kW models. --Srleffler 03:47, 22 February 2007 (UTC)
Where can I buy that 3000000lm/20kW widget? I would like to see the catalog and technical specifications... Perhaps it's a model with the same chemistry as car's xenon headlamps, witch are not exactly "xenon", but only use xenon for a quick start effect. And they don't have the nice and continuous xenon spectra also. --Rnbc 01:51, 24 February 2007 (UTC)
No idea. I hunted online but couldn't find anything. IMAX bulbs consume 15 kW, but they are no more efficient than the 12 kW XBO bulbs.--Srleffler 02:00, 24 February 2007 (UTC)
Well, just consider this: the solar spectra itself has an efficiency of about 100lm/W (a little less), and that's as high as you can get with a blackbody-like spectra. Xenon spectra exibits some UV lines, and some very strong lines in the IR, being otherwise rather flat in the visible, even more flat than a blackbody, so it has more blue and red, lowering efficiency greatly from an ideal blackbody due to all these factors combined. I find it really amazing they can get as high as 50lm/W, let alone 150lm/W: I still think that number is bogus.
I changed the wording to de-emphasize the high value and give a more typical range. I agree with you that the 150 lm/W number is suspicious, but this is original research. The 150 lm/W number is supported by a reference. Before we change it, we should try to find a reference that explicitly gives the range of efficiencies that can be obtained with Xenon (or quotes a value for the highest obtained, etc.). The XBO catalog doesn't do it, since that only tells us what their range is; they don't assert that there aren't more efficient Xenon lamps in existence.--Srleffler 04:12, 25 February 2007 (UTC)
Ok, but let me tell you that the reference mentioning 150lm/W contains no part numbers, no model references, nothing: It's just a number. I wouldn't consider that "reliable". Also, I've looked at a few catalogs (from philips, osram, ushio, hanovia) and found nothing above 50lm/W. I found a few references for 60lm/W when in the context os Xenon-long-arc lamps, but nothing solid with part numbers and model specificaations.
Yes, it's probably just a typo—they probably meant 50 lm/W.--Srleffler 02:52, 26 February 2007 (UTC)

[edit] Tungsten lamp curve

This curve does not accurately reflect the emission of a tungsten lamp for reasons explained in the talk page for Blackbody radiation.[2] Furthermore, it contradicts the text of the article, viz., "...most of its emission is in the infrared." This graph should be removed and replaced by a more accurate one. Drphysics 18:54, 15 March 2007 (UTC)

Link to discussion--Srleffler 20:31, 15 March 2007 (UTC)

[edit] add clarifying details

This is a very important, difficult, and confusing subject. Many lighting-related articles are involved, and share tables as templates. The "Lighting efficiency" table needs more columns, so that those of us trying to make sense of this have some hope. The various sources listed should be characterized with deg-K range etc. The text says that "True luminous efficacy is a property of the radiation emitted by a source" and then leaves us hanging. Please add a column to the table that gives this actual "true luminous efficacy" for each source. Please add the total W radiated by each source, and how much (% or W) of that is in the visible spectrum.

Electric power goes into an incandescent bulb. Some of the energy is radiated. Some of that is in the visible spectrum. Some of that the human eye sees well, some barely at all. That is three levels of nested loss. A fairly simple and important concept. But not clear in the WP lighting articles, and the relevant numbers are not given, only some sorts of "final" numbers that confuse because it is not clear what/which factors they are including how.

The table should probably also list a few monochromatic color sources to help with understanding the color-weighting aspects.

Without an extremely clear exposition of these matters, we cannot understand the "efficiency" aspects of incandescent lighting, nor understand comparisons with other types of lighting.

Also for the fluorescent tubes, we need a note clarifying whether these numbers are for the tubes themselves, or for the whole tube and ballast system as a whole. (And I assume these numbers are not for typical lighting devices installed in typical luminares, which should also be at least mentioned in a footnote, mentioning typical additional losses - these "overall" numbers are not truly "overall" from an applications perspective.) -69.87.201.16 11:01, 25 May 2007 (UTC)

[edit] Add theoretical maximum efficacy for white light?

I notice the theoretical maximum efficiency for lumens per watt is 683. However, this is only for a single monochromatic wavelength of green. Would it not be feasible to add another entry to give the theoretical maximum of white light to around 227.67 (which is basically 683/3)? --Skytopia 06:36, 4 October 2007 (UTC)

Where do you get that number from? It's not clear to me that there even is a theoretical maximum of white light, since it would depend on what your definition of "white" is. In any event, a citation supporting the new information would be required.--Srleffler 17:26, 4 October 2007 (UTC)
Note also that, as mentioned in the article, an "ideal" white light source with a perfectly flat spectrum has a luminous efficacy of 242.5 lm/W, which is higher than your supposed maximum.--Srleffler 13:19, 7 October 2007 (UTC)
Is there any actual WP:RS for this number, or for this concept of an ideal white light source? Does it mean equal energy per wavelength from 400 to 700 nm? Or what? I can find no source that says. Also, what about the maximum luminous efficiency of an ideal blackbody? There must be some temperature at which efficiency is maximized, and the efficiency at that point is well defined and probably well known. Do you know? Looks like maybe near 14.5% at 7000K, but do we have an actual source and actual numbers? Here is a book that says it peaks at 6500K, but doesn't give the efficiency number. Is it possible that the "ideal white light" being discussed is in fact a blockbody, not a flat spectrum? Dicklyon (talk) 01:27, 6 January 2008 (UTC)
I suspect it's equal power per unit frequency in that range, actually. In audio and electronics "white" noise is noise with equal power per unit frequency. Note that the article already gives 95 lm/W at 6300°C as the maximum efficacy for a blackbody, and it cites a source.--Srleffler (talk) 18:23, 6 January 2008 (UTC)
Ah, I see it now. It says 6300 C or 6600 K, which agrees with my calculation. Why does it say "[sic]" in the quote? I don't think you're right on the equal energy per frequency; I've never seen such a thing in talk of optical spectra, but equal per wavelength is common and gives very nearly the answer quoted; still need a source and a better number for that one, though. Dicklyon (talk) 20:53, 6 January 2008 (UTC)
I added the [sic] because he uses "efficiency" to describe what should, in the context of this article, be "efficacy".--Srleffler (talk) 01:28, 7 January 2008 (UTC)
Seems like it implies he said something wrong, when it's really just an alternative usage of a correct term. OK if I take it out? Dicklyon (talk) 01:49, 7 January 2008 (UTC)
No. Given the definitions in this article, his usage is wrong. It would potentially be confusing to have "efficiency" used to mean lm/W without marking it. An alternative might be to do an editorial correction in the quote: "...and the theoretical luminous [efficacy] is 95 lumens per watt."--Srleffler (talk) 05:04, 7 January 2008 (UTC)
I understand it's wrong [sic] per the definitions in the article. But that's not his fault; what he said was correct and consistent, and the "sic" makes it look like we think he said something wrong. It's pretty common to use it that way. Dicklyon (talk) 05:10, 7 January 2008 (UTC)
I just calculated the blackbody max. Based on 1 nm data and simple sums, using 1931 y(lambda) and a matlab blackbody code snippet that I found online, the max luminous efficiency is 13.97% (95.4 lm/W), attained for temps from 6500 to 6700 K (that is, it varies less than 0.01% across that temp range, with a peak near 6630). And I get 243.13 for the mean y(lambda) from 400 to 700 nm, so you're right that the 242.5 number probably does come from a flat spectrum over that range. It would sure be nice to have a source for these things, and maybe better numerics for more definitive numbers. Dicklyon (talk) 03:40, 6 January 2008 (UTC)
Here is a source that says 93 is max, at 6300 K. And here is one that shows the peak at 6600K but doesn't give the exact value, just a plot. And this one says about 6800 K. Dicklyon (talk) 04:08, 6 January 2008 (UTC)
You're right, 242.5 is mentioned higher up the article. I hadn't seen that previously. Do you think it would be a good idea to list it in the lower table as well? I know it's a slight duplicate of information, but it's nice to compare the theoretical maximum against the other white-ish lights in that table. Also, the information 683 lm/W is duplicated as well.
Also in regards to the point that a more efficient white light source can be made more efficient with say... 3 wavelengths, instead of a multitude of wavelengths, I'm not sure that's the case. If it's true, then they've got to be very close in efficiency anyway (do you know the 3 wavelength stat by any chance?)
Finally, I thought the link to Luminosity_function link was appropriate along with the other three. In this kind of article, confusion can stem from the finer points of what lumens actually are, so it's good to include it in there.--Skytopia (talk) 18:06, 29 March 2008 (UTC)
I took it out not just because it's a duplicate, but also because it is misleading. It's not really correct to talk about a "theoretical maximum" efficacy for white light, since "white" is not a well-defined thing. The value we are tossing around (242.5 lm/W) is the luminous efficacy of a perfectly flat spectrum through the visible, with no light outside the visible spectrum. This is "ideal" in the mathematical sense: an idealized or optimally simple form of "white" light. It's not necessarily the best white light source possible. One could make a lamp that produces a nice smooth continuous spectrum that is humped in the middle; something like the luminosity function, but perhaps with not as big a ratio of green to red or blue. Such a source could have an efficacy greater than 242.5 lm/W, and would appear nice and white to an observer.
I removed the extra link to luminosity function, since it already appears in the article. The "see also" section is for linking to relevant pages that are not already linked.--Srleffler (talk) 18:21, 29 March 2008 (UTC)
I think the main reason I would still like the (admittedly somewhat engineered) value for maximum white light efficiency in the main table as well is so that one can see how much more technology can progress before 'white light' efficiency maxes out. You're right that a slight hump towards green will still be considered by the average observer to be more or less 'whitish', but let's assume that 'pure white' (whatever that is) is actually a goal. For that goal, I think the definition of a flat line throughout the visible spectrum fulfils that quite well.
If a light is tinted slightly red, green or blue, it can be difficult for people to see that. But that doesn't make it any less tinted; it's just that the eye has temporarily 'adapted' to that new level as white. However, the illusion is lost more and more as you keep adding more saturation to the light, which is why the best value for perceptive white light would be in the 'middle' of the illusion area (around 6000-6500K). Therefore, this makes perceptive white somewhat an absolute value, as well as just a mere relative one. --Skytopia (talk) 12:53, 16 April 2008 (UTC)
There is nothing special about the flat spectrum. It is neither the maximum in efficiency nor a good definition of "white". It is completely unnatural. Remember that our eyes are designed to see primarily with a ~6500 K blackbody illumination. That strongly-humped spectrum is probably the best definition of what "white" is. A blackbody spectrum truncated to cover only the visible range would probably have a higher luminous efficacy than the flat spectrum, too. The flat spectrum is by no means an indicator of the maximum luminous efficacy that can be achieved by a "white" source.
I think you seriously underestimate the human brain's ability to adapt to different ambient lighting. Our vision system is quite adept at "retuning" to perceive ambient illumination as white, even when the same light would be perceived as quite strongly coloured when compared to more typical illumination. This is not a trick or an illusion—it is an essential feature of how the human vision system works. White is relative.--Srleffler (talk) 04:39, 17 April 2008 (UTC)
I agree with Srleffler, that white is not any particular color. However, once you pick a chromaticity for white, say D50 or D65, or whatever you want, then you have a well-defined optimization problem to find the maximum lumens per watt. It would be interesting to work out. I wonder if that's been done. If not, such original research has no place in the article. Dicklyon (talk) 05:07, 17 April 2008 (UTC)
I study and create optical illusions, so I am well aware of how colours (including white) can fool the visual system. However, if the sensation of '100% white' was relative only, then why is it easy for anyone to tell the difference between illumination of a ~6500K light bulb compared to that of the more orangey 2700K illumination provided by incandescent bulbs? I can be in a room with either illumination for hours, and while my eyes can adapt to each, it only takes a moment's thought to tell which illumination is closer to actual white (whatever that is). Therefore, closer values to the 6000-6500K ballpark would also be distinguishable from 6500K to lesser degrees, even after acclimatization. --Skytopia (talk) 08:07, 17 April 2008 (UTC)

[edit] Luminous efficacy of display screens

I would find it interesting to see figures on luminous efficacy and efficiency of different display technologies. As I understand some of the screens produce light pretty effectively. --Khokkanen 11:14, 7 October 2007 (UTC)

[edit] Comparison of tungsten lamps needed

100Watt tungsten lamps are more efficient than 60Watt lamps. Ordinary "pear shaped" bulbs are more efficient than "candle" bulbs. Quartz is better than glass. 110V lamps are better than 240Volt. Presumably, 12Volt-halogen are better than mains powered halogen. Is this simply to do with the filament temperature, and that a higher-resistance filament must be thinner, therefore must run cooler lest it burn out rapidly? —Preceding unsigned comment added by 81.187.40.226 (talk) 05:31, 14 November 2007 (UTC)


Some extra data points (information from the packaging of the light bulbs), all referring to 220/240V bulbs:

  • A 60 Watt "16x life" (Greenstock) bulb emits 320 lumens, whereas a regular 60 Watt bulb emits 700 lumens, and a HalogenA bulb emits 840 lumens.
  • A 100 Watt GLS "triple-life plus" bulb emits 1120 lumens, whereas a regular "single life" (1000 hour) bulb emits 1330 lumens.
  • A 25 Watt Greenstock 8x candle bulb emits 160 lumens, whereas a 28 Watt Osram "Halogen Energy Saver" candle bulb emits 340 lumens. —Preceding unsigned comment added by 87.194.171.29 (talk) 00:26, 6 January 2008 (UTC)

[edit] Reference no longer exists!

http://www.ts-audio.biz/tsshop/WGS/411/PRD/LFH0324408/Osram_6406330_500mA_52V_E10_BLK1_MINIWATT-Halogen-Gluehlampe_f.Taschenl..htm points to a page which no longer exists. This is currently reference #12 (#11, in German, is dead, too). That is all.65.183.135.231 (talk) 16:47, 2 June 2008 (UTC)

Thanks. I have marked the links as dead.--Srleffler (talk) 17:32, 2 June 2008 (UTC)